Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, most notably Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are toxic and among the most carcinogenic substances known. After entering the body, aflatoxins are metabolized by the liver to a reactive intermediate, aflatoxin M1, an epoxide. Aflatoxin is frequently misspelled as "aflotoxin" and "alfatoxin", which could be confused with alpha toxin.
Aflatoxin-producing members of Aspergillus are common and widespread in nature. They can colonize and contaminate grain before harvest or during storage. Host crops are particularly susceptible to infection by Aspergillus following prolonged exposure to a high humidity environment or damage from stressful conditions such as drought, a condition which lowers the barrier to entry.
The native habitat of Aspergillus is in soil, decaying vegetation, hay, and grains undergoing microbiological deterioration and it invades all types of organic substrates whenever conditions are favorable for its growth. Favorable conditions include high moisture content (at least 7%) and high temperature.
Crops which are frequently affected include cereals (maize, sorghum, pearl millet, rice, wheat), oilseeds (peanut, soybean, sunflower, cotton), spices (chile peppers, black pepper, coriander, turmeric, ginger), and tree nuts (almond, pistachio, walnut, coconut, brazil nut).
The toxin can also be found in the milk of animals which are fed contaminated feed.
Virtually all sources of commercial peanut butter contain minute quantities of aflatoxin, but it is usually far below the US Food and Drug Administration's (FDA) recommended safe level.
No animal species is immune to the acute toxic effects of aflatoxins including humans; however, humans have an extraordinarily high tolerance for aflatoxin exposure and rarely succumb to acute aflatoxicosis.
Chronic, subclinical exposure does not lead to symptoms as dramatic as acute aflatoxicosis. Children, however, are particularly affected by aflatoxin exposure which leads to stunted growth and delayed development. Chronic exposure also leads to a high risk of developing liver cancer, as the metabolite aflatoxin M1 can intercalate into DNA and alkylate the bases through its epoxide moiety. This is thought to cause mutations in the p53 gene, an important gene in preventing cell cycle progression when there are DNA mutations.
Medical research indicates that a regular diet including apiaceous vegetables such as carrots, parsnips, celery and parsley, reduces the carcinogenic effects of aflatoxin.
The first method is measuring the AFB1-guanine adduct in the urine of subjects. Presence of this breakdown product indicates exposure to aflatoxin B1 in the past 24 hours. However, this technique only measures recent exposure, and due to the half-life of this metabolite, the level of AFB1-guanine measured can vary from day to day, based on diet, and thus is not ideal for assessing long term exposure.
Another technique that has been used is a measurement of the AFB1-albumin adduct level in the blood serum. This approach provides a more integrated measure of exposure over several weeks/months.
Aflatoxins M1, M2 were originally discovered in the milk of cows which fed on moldy grain. These compounds are products of a conversion process in the animal's liver. However, aflatoxin M1 is present in the fermentation broth of Aspergillus parasiticus.
Studies have shown that concurrent infection with the Hepatitis B virus (HBV) during aflatoxin exposure increases the risk of hepatocellular carcinoma (HCC). As HBV interferes with the ability of hepatocytes to metabolize aflatoxins, an aflatoxin M1-DNA conjugate exists for a longer period of time in the liver, increasing the probability of damage to tumor suppressor genes such as p53. This effect is synergistic with the resulting damage far greater than just the sum of aflatoxin and HBV . (Williams, 2004)
Decreasing HBV infection levels through vaccination is an effective and simple approach that can be taken to reduce these harmful synergistic effects, thus decreasing the impact of chronic aflatoxin exposure. This strategy may prove to be highly effective – many regions of the world which have high aflatoxin rates, such as western Africa and China, also have high HBV infection rates.
As of May 2008, there are but three primary manufacturers (as distinguished from re-packers and re-sellers) of pure aflatoxins known:
Customers use these compounds for instance as internal standard when monitoring foodstuffs for aflatoxin contaminants.
|
|
|
|
|
|
|
|
|
|
|
|
|